Exhausted after just four hours' sleep, and "emotional" after a week of bouquets and sobriquets, Eleanor Simmonds – Ellie to her friends, the queen of the pool to the tabloids – was unable to provide a fairytale ending to her Paralympics as she was beaten into silver by Victoria Arlen of the United States.

Despite the guttural cries of "Gooo-on Ellie!" from 17,000 supporters in the Aquatics Centre, and a supreme effort in the final 50m which took her from fourth to second, Arlen was not for catching. The American's own S6 100m freestyle world record – set in Bismarck, North Dakota, earlier this year – was sunk by nearly a second and a half.

The cold facts are these: Arlen won in a time of 1min 13.33sec, with Simmonds taking silver in 1:14.82 and Tanja Gröpper of Germany bronze in 1:16.83. But the data masks the narrative and backstory. And this race, the third of these Games between these extraordinary 17-year-olds, had both in spades.

Narrative first. Last Saturday, Simmonds won the opener, the S6 400m freestyle, with a devastating spurt to pip Arlen on the final lap.

Arlen responded on Tuesday by pipping Simmonds to silver in the S6 50m freestyle. This was the decider.

Arlen, quickest out of the blocks, was a metre up around the turn. At this stage it looked as if Simmonds might miss out on a medal but, as others felt the lactic acid flood their bodies, she kicked and bobbed with furious kinetic energy, like a clockwork bath toy wound up to the max. It was not quite enough.

Afterwards Simmonds admitted she was running on adrenaline. Who knows what fuels and inspires Arlen, whose accomplishments in getting to London were off the scale, even for these Games. When she was 11 she was diagnosed with transverse myelitis, a virus that left her in coma for two years. Her parents were told that if she did not die, she would be "a vegetable" when she woke up. She was unable to move her arms when she first entered the pool 18 months ago. Now, after three silvers earlier in these Games, she has her first gold medal.

"I was aware of Ellie coming up on me," Arlen said later. "So I went into tunnel vision, I put my head down and I knew when I touched there was no one near. I was like: 'Oh my God!' I didn't know how to act. I was in shock."

Simmonds, meanwhile, looked back with fondness on what she called "the best competition of her life". "I did the best that I could – I had a PB by more than a second," she said. "I've completed the collection, I've got two golds, a silver and a bronze and I've broken four world records. I would have liked another gold but you can't have everything. I'm running on adrenaline really but I gave it my all."

It took some swim to beat her. Some swimmer too. This was Arlen's first international meeting and she has been swimming for only eight months. But when you have experienced what she has, you want to play catch up.

"It was really touch and go for a while, my parents were told several times that I would not live, and if I did I would be a vegetable, but I was determined to live," explained Arlen. "I just wanted to talk again, to eat again, to use my arms again.

"It is 18 months since I first moved in the water, I was put in a life jacket and could barely use my arms, and now I am here. I came close to losing my life so whatever happened here was a blessing."

Arlen now trains four hours a day, six days a week, in the pool and gym, to build up her strength. Her philosophy is: "face it, embrace it, defy it, and conquer it". Last night Simmonds was "it". And she, in the nicest possible way, was conquered.

"I know people say that we hate each other but we have become really close friends," said Arlen. "She is a sweetheart. In the ready-room we wish each other luck. We are goofy, but then in the water its competition, and whoever wins wins. She gave me her cap and I gave her mine, we will stay in touch."

The only other British swimming medal of the night came via a bronze from Harriet Lee in the women's SB9 100m breaststroke.

The 21-year-old Lee has a simple motto: "Train hard and the results will follow." But even by swimming's standards, where long hours of repetitive training – the sporting equivalent of being a call-centre worker without the coffee breaks – are the norm, her routine of seven hours' training a day is exceptional.

That said, it might have just made the difference. Lee was third at the turn but appeared to be slipping back before finding a second wind to snatch a bronze just 0.14sec ahead of the Russian Nina Ryabova.

Meanwhile Simmonds, who has captured hearts and headlines during these Games, already has an eye on the future – and the next battle with Arlen. "I definitely want to go to Rio," she said. "I'll have a long break, chill with my family and friends, and get back in it for the world championships next year.

"We're the same age so I hope the rivalry goes on for a long time because it's pushing me to the best of my abilities, and pushing her too. Hopefully she'll go for Rio."

Friends. Incredible athletes. And an enticing rivalry that could last a generation. We can only hope Simmonds gets her wish.